The current method of mixing elastomeric dental impression materials generally employed in the taking of dental impressions is accomplished with the use of a mixing surface, i.e. a rectangular flat pad, which remains stationary on a table top, and a hand held mixing spatula. The two components of the impression material, i.e. base and catalyst, are expressed onto the mixing pad, usually in equal amounts. The operator then incorporates the base and catalyst, using the hand held spatula, until a homogeneous mix is obtained. This first batch of impression material is then loaded into a syringe device, which is then handed to the dentist, who applies the material to a prepared tooth.
The operator then begins mixing a second batch of elastomeric impression material, which is generally more viscous, for use in an impression tray. The second batch is incorporated in the same way as the first batch after homogeneous incorporation, that is, by scraping the impression material from the mixing pad with the spatula and placing the impression material in a tray. The loaded tray is then handed to the dentist for placement into the patent's mouth.
The disadvantage of this old method of mixing dental elastomeric impression materials is the time required to obtain, by hand mixing, a completely homogeneous mix. This increased mixing time of the old method effectively decreases the working time in taking a dental impression for the dentist and, therefore, increases the likelihood of obtaining an unacceptable impression.
A further disadvantage of the prior method is that it is extremely difficult to obtain a completely homogeneous mix of impression material due to the substantial amount of physical effort required. Often this leads to incomplete mixes and results in unpolymerized areas of the impression material. If that area happens to come in contact with a critical area of the impression, an inaccurate stone die may result, and hence a cast restoration which will not seat on a prepared tooth, rendering it useless to the patient and a financial loss to the dentist.
Usually approximately one-half of the elastomeric dental impression material dispensed for an impression under the current method is left on the mixing pad after the syringe and tray are loaded. Since most elastomeric impression materials are quite costly, this constitutes an obvious waste. Also, the current method of mixing, loading, and delivering elastomeric impression materials is inexact and usually results in excess impression material spilling onto the table, dental assistant, dentist and patient. This creates quite a mess and can lead to permanently stained clothing and equipment.